In certain applications it would be very beneficial to be able to mechanically extend or spread a spring. High tension helical springs used on the brakes of heavy equipment are very difficult to stretch by hand. However, no conventional tool is capable of spreading such springs. Tools made for standard helical springs tend to break or bend in attempting to spread high tension helical springs and any tool capable of stretching these springs cannot easily install them on the brake shoes.
Conventional methods of reinstalling brake shoes on heavy equipment is time consuming and very difficult for the sole mechanic due to the relative difficulty of stretching the brake shoe return springs. However, brake pads do wear out and must be replaced quite often on heavy equipment, particularly with the advent of non-asbestos brake pads. Therefore, mechanics must by some method frequently reinstall brake shoes with new brake pads.
One method of reinstalling brake shoes entails installing the return springs on the pair of brake shoes prior to installing the brake shoes on the backing plate of the brake assembly. This then requires the mechanic to lift the joined pair of brake shoes onto the backing plate while aligning the backing plate pins, S cam, rollers, and springs. A pair of brake shoes generally has a mass of well over 20 kilograms (44 pounds), in some cases over 40 kilograms. Lifting and aligning both brake shoes together is a very difficult task for a sole mechanic.
Another method of reinstalling brake shoes entails installing one brake shoe at a time on the backing plate then attaching the brake return spring to each brake shoe with the rollers removed (rollers not against the S cam). This then requires the mechanic to pull on each brake shoe by hand (thereby stretching the brake return spring) and drop the rollers into the notch in each brake shoe and against the S cam. This is very difficult, particularly while dropping the last roller into the notch. Many times this procedure results in smashed finger tips as the mechanic releases the brake shoe.
It would be very desirable to be able to install brake shoes quickly and easily without encountering the above problems. More particularly, it would be very desirable to be able to mechanically stretch the brake return spring and attach it to each brake shoe.